Hubble spies more extra-solar planets

The Hubble Space Telescope has spied sixteen candidate extra-solar planets during a survey of 180,000 stars in the central bulge of the Milky Way galaxy. The findings suggest there could be as many as six billion Jupiter-sized planets in our galaxy.

The candidates were all identified during the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS), using the transit technique - watching for a slight dimming of the star that would have been caused by a planet passing in front of it.

Only two of the planets are bright enough to be confirmed as planets independently, and NASA says researchers worked hard to rule out any other possible causes of the dimming. The remainder will have to wait until the more powerful James Webb telescope is launched in 2011.

Five of the newly spotted planets orbit their stars in less than a day - faster than any that have been identified before. NASA has dubbed these "ultra-short-period-planets".

The fastest goes around its star in 10 hours, and orbits just 740,000 miles out.

"This star-hugging planet must be at least 1.6 times the mass of Jupiter, otherwise the star's gravitational muscle would pull it apart," said SWEEPS team member Mario Livio. "The star's low temperature allows the planet to survive so near to the star."

"Ultra-Short-Period Planets seem to occur preferentially around normal red dwarf stars that are smaller and cooler than our sun," team leader Kailash Sahu of the Space Telescope Science Institute explained. "The apparent absence of USPPs around sun-like stars in our local neighbourhood indicates that they might have evaporated away when they migrated too close to a hotter star." ®